Citigroup is preparing to nominate four financial experts, including two former bank chief executives, to be directors as part of the overhaul of the New York company's board, according to people familiar with the matter.

Citigroup also is likely to add at least one more director with a risk-management background, likely a finance professor.

While the nominations aren't official yet—Citigroup's board hasn't formally backed the picks, and they will be subject to a shareholder vote—the company is expected to announce the boardroom changes by early next week, when it files its annual proxy statement with securities regulators.

As part of the filing, Citigroup also is likely to disclose that current directors Kenneth Derr and Franklin Thomas will step down because they have reached the board's retirement age of 72, these people said. Three other Citigroup directors already have said they will step down.

The expected changes follow months of intensifying pressure from federal officials, who have been pushing new Citigroup chairman Richard Parsons to oust some longtime directors and recruit new ones.

Last month, the US government agreed to expand its stake in Citigroup to as much as 36% of the company's outstanding shares. As part of that deal, the board agreed to be comprised of "a majority of new independent directors as soon as feasible," according to a statement from Mr. Parsons.

The 15-person board has come under fire from regulators, shareholders, employees and even some top Citigroup executives for failing to adequately oversee the company as it took on greater risk. That set the stage for net losses totalling more than $37bn in the past five quarters.

Mr. Parsons, a former Time Warner Inc. CEO who ran a New York thrift in the 1990s, is the only outside director at Citigroup with a financial services background.

Citigroup has been trying for months to lure new blood to its board, but the process has been stymied by reluctance among potential candidates. Citigroup has tried to overcome the snags by pitching the director slots as a "national obligation," according to a person who has spoken with several people who were approached.

Mr. Grundhofer, who stepped down as US Bancorp's chairman in December 2007, previously turned down overtures by Citigroup, according to a person close to him. It isn't clear what led Mr. Grundhofer to reconsider his initial hesitance. Mr. Grundhofer didn't respond to requests for comment.

Mr. O'Neill was chief financial officer at BankAmerica Corp., the San Francisco bank that merged with NationsBank Corp. a decade ago to form Bank of America Corp. In 1999, Mr. O'Neill became CEO of Barclays PLC, but resigned from the UK bank in 2000 for health reasons. About seven months later, he was named CEO of Bank of Hawaii. Mr. O'Neill couldn't be reached for comment.

Mr. Parsons has been trying to persuade some current directors to step down, according to people familiar with the matter. But some of those directors are resisting because they don't want to be seen as scapegoats for Citigroup's problems, these people said.

—Write to David Enrich at david.enrich@wsj.com, Robin Sidel at robin.sidel@wsj.com and Joann S. Lublin at joann.lublin@wsj.com; Dan Fitzpatrick contributed to this article.